Most polymer resins are manufactured by polymerizing monomers using initiators. The polymerization may be generally classified into an endothermic reaction and an exothermic reaction. For example, it is necessary to remove reaction heat generated in an exothermic reaction, such as polyvinyl chloride (PVC) polymerization, thereby improving the efficiency of the reaction.
Factors affecting the productivity are various in a practical process for manufacturing polymer resin by polymerization. In polymerization accompanied by heat generation, controlling the reaction temperature is one of the most important factors. Consequently, a cooling system for removing reaction heat is essential in an exothermic polymerization system. A typical example of the cooling system is illustrated in FIG. 1.
Referring to FIG. 1, an exothermic polymerization system 10 includes a reactor 20 in which polymerization of monomers is carried out and a cooling system comprising a jacket 30 mounted at the wall of the reactor 20 and a reflux condenser 40 mounted at the top end of the reactor 20. A coolant circulates through the jacket 30 and the reflux condenser 40 to remove heat of polymerization generated in the reactor 20. The reflux condenser 40 allows vapor existing at the upper end of the reactor 20 to contact the coolant so as to lower the temperature of the reactor 20 to a predetermined range of temperature.
Consequently, in the exothermic polymerization system 10 as shown in FIG. 1, the temperature of the coolant in the jacket 30 and the reflux condenser 40 is controlled to the predetermined range of temperature, thereby accomplishing optimum operating conditions.
Meanwhile, in the exothermic polymerization system, the heat generation amount may be decided by various factors. Typical examples of the factors may be polymerization degree and polymerization rate. These factors have close relation to the reaction temperature and the addition amount of the initiator. Especially, there is a complex correlation therebetween. Consequently, it is possible to improve the productivity through the adjustment of the related factors.
In connection with this matter, U.S. Pat. No. 6,440,374 discloses a technology for setting optimum reaction conditions by operating a cooler surrounding a reactor in a reaction system such that the temperature measured by a temperature sensor, which is mounted between the reactor and the cooler, is equal to a predetermined temperature level. This technology is the most generally considerable productivity improving method. However, this technology has a problem in that the temperature of cooling water must be controlled depending upon heat of reaction. Especially, in a polymerization system in which normal industrial water is used as the cooling water, it is necessary to use an additional apparatus for controlling the temperature of the cooling water and energy for operating the additional apparatus. As a result, the costs are increased although the productivity is improved.
On the other hand, Korean Unexamined Patent Publication No. 1993-019701 discloses a polymerization method of adding an initiator and a monomer in a reactor in polymerization conditions using a monomer supply profile and an initiator supply profile. Specifically, the supply profiles decide the ratio of monomer concentration to initiator concentration according to polymerization kinetics and the reaction temperature, the initiator concentration and the monomer concentration, and polymerization degree selected for a polymer. Also, the ratio of the monomer concentration to the initiator concentration decided according to the kinetics relationship is changed, by a polymerization efficiency factor, so as to obtain polymerization degree of approximately uniform concentration during the polymerization, thereby obtaining a polymer having uniform polymerization degree. This method is a technology for obtaining a polymer having uniform polymerization degree, i.e., a technology for adjusting the initiator concentration and the monomer concentration under certain conditions. However, information about the improvement of the productivity in the exothermic polymerization system in which the removal of heat of reaction is important is not taught or suggested in the above-described publication.
Consequently, a technology for improving the productivity by reducing the energy consumption amount while using the conventional polymerization system is in great demand. In connection with this case, it may be preferable to have a technology for controlling the temperature of the polymerization system by using normal industrial water as a coolant without additionally controlling the temperature of the coolant.
For instance, a polyvinyl chloride (PVC) resin is manufactured by polymerization accompanied by heat generation. The preferable polymerization temperature of the PVC resin is 40 to 80° C. depending upon the polymerization degree thereof. Consequently, the reaction temperature is controlled by directly using industrial water, which is not additionally cooled, as a coolant. The temperature of the cooling water (industrial water) is not additionally controlled. As a result, the temperature of the cooling water may be decided by seasonal factors. For example, the temperature of the cooling water is low in the winter season, and therefore, the amount of heat removable from the reactor through 1-time circulation (the heat removal amount) is large. In the summer season, on the other hand, the heat removal amount is relatively small. In the same seasonal conditions, the heat removal amount is relatively large in the forenoon.
Consequently, the existing exothermic polymerization system is constructed in a structure in which the improvement of the productivity according to the temperature difference of the cooling water is not expected although the difference of the heat removal amount is changed depending upon the temperature of the cooling water. Specifically, the polymerization rate may be increased (the reaction time may be decreased) to improve the productivity in the cooling water temperature condition in which the heat removal amount is large. However, the conventional art does not provide a technical proposal in connection with the above-described matter.